docs: def Montillet_Akkari_Comiti(dp, voidage, vs, rho, mu, L=1, Dt=None):
      r'''Calculates pressure drop across a packed bed of spheres as in [2]_,
      originally in [1]_. Wall effect adjustment is used if `Dt` is provided.
  
      .. math::
          \frac{\Delta P}{L\rho V_s^2} D_p \frac{\epsilon^3}{(1-\epsilon)}
          = a\left(\frac{D_c}{D_p}\right)^{0.20}
          \left(\frac{1000}{Re_{p}} + \frac{60}{Re_{p}^{0.5}} + 12 \right)
  
      .. math::
          Re_{p} = \frac{\rho v_s  D_p}{\mu}
  
      Parameters
      ----------
      dp : float
          Particle diameter of spheres [m]
      voidage : float
          Void fraction of bed packing [-]
      vs : float
          Superficial velocity of the fluid (volumetric flow rate/cross-sectional 
          area)[m/s]
      rho : float
          Density of the fluid [kg/m^3]
      mu : float
          Viscosity of the fluid, [Pa*s]
      L : float, optional
          Length the fluid flows in the packed bed [m]
      Dt : float, optional
          Diameter of the tube, [m]
  
      Returns
      -------
      dP : float
          Pressure drop across bed [Pa]
  
      Notes
      -----
      :math:`10 < REp <2500`
      if Dc/D > 50, set to 2.2.
      a = 0.061 for epsilon < 0.4, 0.050 for > 0.4.
  
      Examples
      --------
      Custom example:
  
      >>> Montillet_Akkari_Comiti(dp=0.0008, voidage=0.4, L=0.5, vs=0.00132629120, rho=1000., mu=1.00E-003)
      1148.1905244077548
  
      References
      ----------
      .. [1] Montillet, A., E. Akkari, and J. Comiti. "About a Correlating
         Equation for Predicting Pressure Drops through Packed Beds of Spheres
         in a Large Range of Reynolds Numbers." Chemical Engineering and
         Processing: Process Intensification 46, no. 4 (April 2007): 329-33.
         doi:10.1016/j.cep.2006.07.002.
      .. [2] Allen, K. G., T. W. von Backstrom, and D. G. Kroger. "Packed Bed
         Pressure Drop Dependence on Particle Shape, Size Distribution, Packing
         Arrangement and Roughness." Powder Technology 246 (September 2013):
         590-600. doi:10.1016/j.powtec.2013.06.022.
      '''
      Re = rho*vs*dp/mu
      if voidage < 0.4:
          a = 0.061
      else:
          a = 0.05
      if not Dt or Dt/dp > 50:
          Dterm = 2.2
      else:
          Dterm = (Dt/dp)**0.2
      right = a*Dterm*(1000./Re + 60/Re**0.5 + 12)
      left = dp/L/rho/vs**2*voidage**3/(1-voidage)
      return right/left